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%I #44 Mar 13 2022 09:49:55
%S 1,1,2,6,19,71,300,1370,6563,32272,161700,820166,4198764,21647353,
%T 112262033,585049063,3061951973,16084816384,84773694223
%N a(n) is the number of free polyominoes with k cells and n-k distinguished vertices.
%C This sequence counts "free" polyominoes where holes are allowed. This means that two polyominoes are considered the same if one is a rigid transformation (translation, rotation, reflection or glide reflection) of the other.
%C A000105(n) <= a(n) <= A343577(n).
%C For an ordinary, asymmetrical polyomino, the number of free polyominoes with d distinguished cells is equal to C(v,d), where v is the number of vertices of the polyomino, and C is the binomial coefficient (A007318). - _John Mason_, Mar 11 2022
%H Peter Kagey, <a href="/A343417/a343417_1.hs.txt">Haskell program for computing sequence</a>.
%e For n = 3, the a(3) = 6 polyominoes with k cells and 3-k distinguished vertices are:
%e +---+ *---+ +---+
%e | | | | | |
%e + +---+ +---+---+---+ + + * + *---+ *---+
%e | | | | | | | | | | | |
%e +---+---+, +---+---+---+, +---+, +---+, *---+, +---*,
%e where distinguished vertices are marked with asterisks.
%e For n = 4, a(4) = 19 because there are A000105(4) = 5 polyominoes with four cells and no distinguished vertices, 7 polyominoes with three cells and one distinguished vertex, 6 polyominoes with two cells and two distinguished vertices, and 1 polyomino with one cell and three distinguished vertices.
%Y Cf. A000105, A343577.
%K nonn,more,hard
%O 0,3
%A _Peter Kagey_, Apr 15 2021
%E a(11)-a(18) from _John Mason_, Mar 11 2022